CONTRIBUIÇÃO DA GEOQUÍMICA DAS TERRAS RARAS À CARACTERIZAÇÃO DOS CARBONATITOS DA FAZENDA VARELA, LAGES, SC

Abstract

As a part of a petrological and geochemical study the distribution of the rare earth elements in Fazenda Varela carbonatites was discussed. These carbonatites were the first described in Lages Dome. Santa Catarina State, Brazil. They intruded and fenitized sedimentites of the Tubarão Group; the fenitizing fluids are dominantly potassic. The main constituents of the carbonatites are ankerite, barite, K feldspar, and synchisite; secondary apatite is rare. High Ba/Sr, Nb/Ta, and Th/U ratios are conspicuous. The concentration of the rare earth elements is very high relative to the concentration in chondrites, the mean in the earth crust and even in most carbonatites; normalized distribution curves show higher concentration of the light lanthanides (Ce group) in comparison with the heavy lanthanides (Y group). In addition to other petrological and geochemical features, high absolute and relative concentrations of the light lanthanides indicate that these carbonatites represent the last phases of carbonatitic fractionation and reinforce, the possibility of occurence of carbonatites from the early phases of crystallization at the Lages alkaline district.